Gastrointestinal (“GI”) motility regulates the orderly movement of ingested material through the gut to ensure adequate absorption of nutrients, electrolytes, and fluids. Proper transit of the GI contents through the esophagus, stomach, small intestine, and colon depends on regional control of intraluminal pressure and several sphincters, which regulate their forward movement and prevent back-flow. The normal GI motility pattern may be impaired by a variety of circumstances, including disease and surgery.
GI motility disorders include gastroparesis and gastroesophageal reflux disease (“GERD”). Gastroparesis, whose symptoms include stomach upset, heartburn, nausea, and vomiting, is the delayed emptying of stomach contents. GERD refers to the varied clinical manifestations of the reflux of stomach and duodenal contents into the esophagus. The most common symptoms are heartburn and dysphasia, with blood loss from esophageal erosion also known to occur. Other examples of GI disorders in which impaired GI motility is implicated include anorexia, gall bladder stasis, postoperative paralytic ileus, scleroderma, intestinal pseudo-obstruction, irritable bowel syndrome, gastritis, emesis, and chronic constipation (colonic inertia).
Motilin is a 22-amino acid peptide hormone secreted by endocrine cells in the intestinal mucosa. Its binding to the motilin receptor in the GI tract stimulates GI motility. The administration of therapeutic agents that act as motilin agonists (“prokinetic agents”) has been proposed as a treatment for GI disorders.
The erythromycins are a family of macrolide antibiotics made by the fermentation of the actinomycetes Saccharopolyspora erythraea. Erythromycin A, a commonly used antibiotic, is the most abundant and important member of the family.

The side effects of erythromycin A include nausea, vomiting, and abdominal discomfort. These effects have been traced to motilin agonist activity in erythromycin A (1) and, more so, its initial acid-catalyzed degradation product (5). (The secondary degradation product, spiroketal (6), is inactive.)

Spurred by the discovery of motilin agonist activity in erythromycin A and degradation product 5, researchers have endeavored to discover new motilides, as macrolides with prokinetic activity are called. Much of the research has centered on generating new erythromycin analogs, either via post-fermentation chemical transformation of a naturally produced erythromycin or via modification (including genetic engineering) of the fermentation process. Illustrative disclosures relating to motilides include: Omura et al., U.S. Pat. No. 5,008,249 (1991) and U.S. Pat. No. 5,175,150 (1992); Harada et al., U.S. Pat. No. 5,470,961 (1995); Freiberg et al., U.S. Pat. No. 5,523,401 (1996); U.S. Pat. No. 5,523,418 (1996); U.S. Pat. No. 5,538,961 (1996); and U.S. Pat. No. 5,554,605 (1996); Lartey et al., U.S. Pat. No. 5,578,579 (1996); U.S. Pat. No. 5,654,411 (1997); U.S. Pat. No. 5,712,253 (1998); and U.S. Pat. No. 5,834,438 (1998); Koga et al., U.S. Pat. No. 5,658,888 (1997); Miura et al., U.S. Pat. No. 5,959,088 (1998); Premchandran et al., U.S. Pat. No. 5,922,849 (1999); Keyes et al., U.S. Pat. No. 6,084,079 (2000); Ashley et al., US 2002/0025936 A1 (2002); Ashley et al., US 2002/0094962 A1 (2002); Carreras et al., US 2002/0192709 A1 (2002); Ito et al., JP 60-218321 (1985) (corresponding Chemical Abstracts abstract no. 104:82047); Santi et al., US 2004/138150 A1 (2004); Carreras et al., US 2005/0113319 A1 (2005); Carreras et al., US 2005/0119195 A1 (2005); Liu et al., US 2005/0256064 A1 (2005); Omura et al., J. Antibiotics 1985, 38, 1631-2; Faghih et al., Biorg. & Med. Chem. Lett., 1998, 8, 805-810; Faghih et al., J. Med. Chem., 1998, 41, 3402-3408; Faghih et al., Synlett., July 1998, 751; and Lartey et al., J. Med. Chem., 1995, 38, 1793-1798. The disclosures of all of foregoing documents are incorporated herein by reference.
Also potentially pertinent are other erythromycin scaffold compounds, even where not designed to be motilin agonists, illustrative disclosures being: Krowicki et al., U.S. Pat. No. 3,855,200 (1974); Radobolja et al., U.S. Pat. No. 3,939,144 (1976); Kobrehel et al., U.S. Pat. No. 3,983,103 (1976); Toscano, U.S. Pat. No. 4,588,712 (1986); Agouridas et al., U.S. Pat. No. 5,444,051 (1995); Agouridas et al., U.S. Pat. No. 5,561,118 (1996); Agouridas et al, U.S. Pat. No. 5,770,579 (1998); Asaka et al., U.S. Pat. No. 6,169,168 B1 (2001); Kobrehel et al., DE 2,402,200 (1974); Pliva Pharmaceuticals, GB 1,416,281 (1975); Pliva Pharmaceuticals, GB 1,461,032 (1977); Asaga et al., JP 2002/241391 (2002); Ryden et al., J. Med. Chemistry, 1973, 16 (9), 1059-1060; Naperty et al., Roczniki Chemii, 1977, 51 (6), 1207-10; Kobrehel et al., Eur. J. Med. Chemistry, 1978, 13 (1), 83-7; Egan et al., J. Antibiotics, 1978, 31 (1), 55-62; Matijasevic et al., Croatica Chemica Acta, 1980, 53 (3), 519-24; Radobolja et al., Croatica Chemica Acta, 1985, 58 (2), 219-25; Hunt et al., J. Antibiotics, 1989, 42 (2), 293-298; Myles et al., J. Org. Chem., 1990, 55, 1636-1648. The disclosures of all of foregoing documents are incorporated herein by reference.
Those skilled in the art will understand that a number of parameters are relevant to the development of motilides. Firstly, the evolution of the erythromycin scaffold in the natural producing organisms has been driven by antibacterial efficacy and not by prokinetic efficacy. Therefore, considerable room remains for optimization of the structure-activity relationship for motilin agonists. Secondly, it is in fact undesirable for a motilide to possess antibacterial activity. The GI tract is host to a large population of bacteria, whose exposure to a motilide having antibacterial activity may induce the development in them of resistance to erythromycin antibiotics. Or, a motilide having anti-bacterial activity may kill beneficial gut bacteria. Thus, a motilide desirably has enhanced prokinetic activity engineered in and antibacterial activity engineered out. Thirdly, a drawback commonly found among motilides evaluated to date is their propensity to desensitize the motilide receptor, meaning that, after the initial dose, subsequent doses of a motilide elicit a weaker or no response (tachyphylaxis). Fourthly, stability and bioavailability are concerns—witness the ready degradation of erythromycin A in the stomach and the lack of activity of its secondary degradation product. Fifthly, some compounds in the erythromycin family have been reported to have undesirable pro-arrhythmic effects, including the prolongation of the QT interval and the induction of ventricular arrhythmias. Limiting these effects to an acceptable level is desirable. Thus, there exists a continuing need to develop new motilides, balancing the various different performance requirements.
Liu et al., US 2006/0270616 A1 (2006), incorporated herein by reference (hereinafter the “Liu '616 application”), discloses a family of motilides represented by the general formula I, wherein RA, RB, RC, RD, and RE are structural variables. A specific compound disclosed there is compound (Ia), which possesses an attractive balance of properties for a motilide.

Once a compound has been selected for development as a possible clinical candidate, consideration must be given to formulating it in an appropriate pharmaceutical formulation. In turn, this means consideration must be given to the possible existence of polymorphs. If polymorphs exist, they may differ in their pharmaceutically relevant properties, including solubility, storage stability, hygroscopicity, density, and bioavailability. One polymorph may more or less spontaneously convert to another polymorph during storage. As a result of such conversion, a formulation designed to deliver a particular polymorph may end up containing a different polymorph that is incompatible with the formulation. A hygroscopic polymorph may pick up water during storage, introducing errors into weighing operations and affecting handleability. A preparation procedure designed for use with a particular polymorph may be unsuitable for use with a different polymorph. Even if no interconversion occurs, one polymorph may be easier to formulate than another, making selection of the right polymorph critical. Thus, polymorph choice is an important factor in designing a pharmaceutical formulation. (As used herein, the term “polymorph” includes amorphous forms and non-solvated and solvated crystalline forms, as specified in guideline Q6A(2) of the ICH (International Conference on Harmonization of Technical Requirements for Registration of Pharmaceuticals for Human Use)).